The invention relates to a device for deflecting a flow of engine exhaust gas, according to the operating condition of the engine, either to one line leading to the atmosphere through the muffler, or to another line directing the flow back through a heat exchanger in the engine to preheat the intake air/fuel mixture, and then out through the muffler to the atmosphere.
In order to improve the performance of an internal combustion engine, especially when the engine is cold, the air/fuel mixture in the carburetor may be preheated by means of the exhaust gases leaving the engine. It is not, however, always desirable to preheat the intake mixture. For example, when operating the engine at full load condition, it is desirable to provide the engine with as much fuel as possible. Preheating, under this operating condition, results in expansion of the intake mixture, which results in less fuel being provided to the cylinder and subsequent power loss.
As a means to control the supply of hot exhaust gases to the heat exchanger, a deflecting flap may be arranged in the exhaust line and positioned to supply exhaust flow either to the heat exchanger, or to the muffler, depending upon the operating state of the engine. In such an arrangement, difficulties result because the exhaust, due to its high temperature, is corrosive, and it also carries a number of contaminants deriving from the combustion residue. Thus, in order to provide a deflecting flap which will be durable with extended engine use, the flap must be able to withstand these extreme operating conditions, and a refractory and costly material must be used.